1. Field of the Invention
The invention relates to a method for producing coated particles according to claim 1.
2. Description of the Related Art
Coated particles are known from German Patent Application Published for Opposition 2 011 306. These particles can among other things consist of a core composed of an inorganic compound of a metal or semimetal, e.g. metal oxides or semimetal oxides such as Al2O3, Zr2O3 or SiO2, and a shell. A polymerized organic compound such as a polyvinyl or polystyrene is suggested for the shell.
Similar particles are known from British Patent 1,006,753. The aforementioned particles also comprise a core, composed of a metal compound and a shell of poly (p-xylene), produced through a partial pyrolysis of cyclical di-p-xylene.
German Patent 94 03 581 U describes coated nano-powder, consisting of a core with a diameter of 3 to 50 nm of a compound containing a metal and a non-metal, as well as a shell consisting of a compound of a different metal with a non-metal. A device for producing the nano-powder, which utilizes a microwave plasma, is described in detail.
The French references FR-A-2 353 621 and FR-A-2 353 622 disclose particles that are preferably made of substances containing silicon oxide and coated with a carbon-containing coating. The coating is produced through catalytic cracking, e.g. of propylene, at temperatures between 250xc2x0 and 1000xc2x0 C. The coated particles serve as filler materials for rubber.
French reference FR-A-2 336 456 discloses coated pigment particles. Glass, talcum, silica gel or aluminum oxide or TiO2-coated mica flakes are mentioned among other things as substrate. The shell consists of soot, which is precipitated out together with metal hydroxides, metal oxides or bismuth oxychloride.
German Patent 196 38 601 C1 discloses a method for producing particles with a core combining a metal with a non-metal and a shell, composed of a polymerized organic compound. With this method, metal compounds that can be evaporated and a reaction gas are made to react in a microwave plasma, wherein the core is produced. The UV light of the microwave plasma polymerizes the shell onto the core. These particles are nano particles with a core diameter of 3 to 100 nm and a shell thickness of 1 to 20 nm.
Under the keyword xe2x80x9cAerosil(copyright),xe2x80x9d the Rxc3x6mpp Chemical Dictionary describes amorphous, spherical particles of xe2x80x9cpyrogenicxe2x80x9d silicic acid with a diameter of 10 to 20 nm, which serve as filler materials for rubber.
Under the keyword xe2x80x9csoot,xe2x80x9d the Rxc3x6mpp Chemical Dictionary furthermore provides the information that tire manufacturers in particular utilization soot as filler material for elastomer. Soot is produced through an incomplete combustion of, for example, aromatic hydrocarbons with a sooty flame that bums in an oxygen-poor atmosphere.
It is the object of the invention to suggest a method for producing particles that can chemically bind just as easily as soot with polymeric phases, particularly rubber, and show improved abrasion behavior. The particles should be distributed homogeneously in the polymeric phase and, as a result of the chemical binding, should not separate out again during the deformation of rubber. The method is designed in particular to permit the production of nano particles.
This object is solved with the method described in claim1. The additional claims contain preferred embodiments of the method.
The abrasion behavior can be improved considerably through the binding of hard particles with polymeric phases, particularly rubber. The abrasion behavior plays an important role, especially for vehicle tires.
Inorganic particles, particularly ceramic particles, cannot be distributed homogeneously in polymeric phases without being subjected to a pretreatment because they do not chemically bind with the polymeric phase.
According to the invention, coated particles are produced, which consist of a core combining a metal or semimetal with a non-metal, which core is surrounded by a shell made of soot. Owing to the soot shell, the coated particles can bind in the same way as soot with polymeric phases, particularly rubber for motor vehicle tires. As compared to soot alone, however, the particles have the advantage that the abrasion resistance of the polymeric phase is increased owing to its hard core.
The core of the coated particles preferably consists of a ceramic. Preferred is a core of silicon dioxide. However, the core can also consist of other hard materials, e.g. silicon nitride, aluminum oxide or zircon dioxide. Particularly preferred are coated nano particles with a core size of less than 100 nm, especially approximately 3 to 50 nm. Especially favorable qualities are expected when using such nano particles. The selection of the soot shell thickness is virtually optional. In practical operations, it results from the production method used.
Suitable as production method in particular for nano particles is the conversion in a microwave plasma. For this, particles consisting of a compound of a metal or semimetal with a non-metal are converted in a first processing step to an aerosol form. This processing step is preferably carried out with the method described in German Patents 196 38 601 C1 and 94 03 581 U. These two documents provide a detail description of a suitable device and a suitable method for producing cores of coated nano particles, wherein the produced cores are simultaneously put into aerosol form. For the processing of larger cores, however, the production methods specified in the remaining cited references are suitable as well.
The particles are subsequently brought into contact with a gas containing at least one aromatic compound. In particular benzol and benzol derivatives such a toluene, xylene or creosol are suitable as aromatic compounds because of their high vapor pressure. However, multi-core aromatic substances such as naphthalene and its derivatives can also be used. The share of aromatic compounds in the gas should be approximately 5 to 10 volume percent.
The particles present in aerosol form are subsequently guided together with the gas through the plasma zone of a microwave plasma, wherein the particles are provided with a soot shell. Experiments have shown that the soot shell produced in this way still contains residual bonds to hydrogen ions, which in particular make it easier to bind with rubber.
If a metallocene is additionally added to the gas, the yield relative to the carbon share can be increased noticeably. In particular ferrocene [Fe(C5H5)2] or magnesocene [Mg(C5H5)2] are suitable as metallocenes. The metallocene share in the organic phase preferably amounts to 10 to 20 weight percent.
The coated particles obtained with the production method, described herein, are suitable in particular as additive for polymeric phases, above all rubber, and as additive for the production of motor vehicle tires. A considerable improvement in the abrasion behavior can be expected.